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    <title>Document</title>
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    <script type="text/javascript">
        //  使用递归求到20的斐波那契数列之和 
        // let count=0
        // function fn(n){
        //     count++
        //     if(n==1 ||n==2){
        //        return 1
        //     }else{ 
        //         return fn(n-1) + fn(n-2)
        //     }
        // }
        // console.log(fn(8));
        // console.log(count);
        
    var count = 1;
    var a = 0;
    var b = 1;
    var c = 0;
    function fn(n) {
        c++
        n=a+b
        count+=n
        if(c == 20){
            return count
        }
        a=b
        b=n
        return fn(n)
}
    console.log(fn());


    </script>
</body>
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